1. Field of the Invention
The present invention relates generally to an electronic circuit module, an electronic circuit module connecting structure and connecting member, and a method for connecting same, and more particularly to an electronic circuit module and an electronic circuit module connecting structure and connecting member used in baseband optical transmission and which operates at an operating frequency in the range of several tens of gigaHertz (GHz), and a method for connecting same.
2. Description of the Related Art
In recent years, as the transmission capacity of optical transmission communications systems (hereinafter optical communications systems) has increased there has been a concomitant increase in the transmission speed of such optical communications systems. For example, research into a 40 Gbps transmission speed system device is accelerating at a number of research institutes and communications concerns, and 10 Gbps optical communications systems (hereinafter 10 Gbps systems) are approaching the commercial-use stage.
In the 10 Gbps systems, microwave band technology has been adapted for use with optical modules. Unlike the case with microwave bands, however, these 10 Gbps systems, because they operate at several tens of Gbps, require the characteristics of the amplifier be such as to amplify a broad band of frequencies ranging from several tens of KHz to several tens of GHz. Accordingly, where this technology is used it is necessary to minimize the impedance mismatching that is otherwise not a problem in the microwave band so that amplification characteristics do not deteriorate at the connections between electronic circuit modules connected in multiple stages.
FIG. 1 shows the structure of an O/E (opto-electric converter) module of a typical optical module. The O/E module comprises an optical element 1, an equalizing amplifier 2, a limiter amplifier 3, a discriminator 4, a timing extractor 5, a timing filter 6 and a second limiter amplifier 7. An optical input signal is received by the optical element 1 and data and clock are output by the discriminator 4.
A description will now be given of an operation of the conventional optical module shown in FIG. 1. A weak optical signal is transmitted along the transmission path (an optical fiber), received at the optical element 1 and converted from light to electricity. Undesirable high-frequency noise is deleted by the equalizing amplifier and the signal is then amplified by the limiter amplifier or the AGC (Automatic Gain Control) amplifier to an amplitude capable of being recognized. At the same time, the clock component is extracted by the timing extractor 5 from the output signal of the equalizing amplifier 2. The clock signal is then replayed by the timing filter 6, the timing filter comprising either a SAW (Surface Acoustic Wave) or a dielectric device and amplified to a predetermined amplitude by the second limiter amplifier 7. The discriminator 4 recognizes the "0"s and "1"s of the data signal by using the clock that replayed the data from the limiter amplifier 3 with a timing extraction circuit 8.
Given the scale of density of current integrated circuits (hereinafter ICs or chips), the structure of this circuit in the region of several Gbps typically comprises two or three chips. As previously noted, however, the introduction of microwave technology is required in the region of several Gbps and leads to the following problems.
First, the resonance frequency of the package must be placed outside the signal band, and thus the package itself must be made compact. As a result, the number of functions that can be included in the package is limited.
Second, in order to obtain isolation of the output signal and the input signal, the gain that can be obtained by one package is limited. Otherwise, if the gain is large, then there is a possibility that the isolation will be broken.
At present, the problems described above are solved by dividing the O/E module internal functions among several electronic circuit modules. FIG. 2, for example, is a diagram of the functional structure of a typical optical module in which the O/E internal functions have been divided among several electronic circuit modules. The equalizing amplifiers 21, 22 and 23 of FIG. 2 correspond to the equalizing amplifier 2 of FIG. 1, the differentiation circuit 51 and full wave rectifier circuit 52 of FIG. 2 correspond to the timing extractor 5 of FIG. 1 and the limiter amplifiers 71 through 74 of FIG. 2 correspond to the limiter amplifier 7 of FIG. 1. Of these, the circuit blocks in double outline represent modularized electronic circuit modules (high-speed electrical modules). Except for clock CLK being output from the limiter amplifier 74, the operation of the device shown in FIG. 2 is identical to the operation of the device shown in FIG. 1.
FIG. 3 shows a portion of a structure in which these electronic circuit modules are connected in multiple stages. An electronic circuit module 31 is mounted on an aluminum housing 33, and at least some of the electronic circuit modules are connected to each other and to a connection substrate with gold ribbon bonding 30. At least some of the electronic circuit modules are connected by a high-speed connection substrate. A low-speed substrate 34 is provided on a bottom portion of the aluminum frame 33.
FIG. 4 shows various top, front and side views of the electronic circuit module of FIG. 3 hermetically sealed. The electronic circuit module has a main body 44 to which are attached two pedestals 45, 46, and a power source terminal 43. The two pedestals 45, 46 each have mounting screw holes 42 and signal lines 41, the signal lines positioned atop ceramic terminals 40.
A description will now be given of the problems with the conventional apparatus equipped with the electronic circuit bed above, with reference to FIG. 5 and FIG. 6. In these diagrams, 63 and 83 denote a microstrip line terminal and 64 and 84 denote an aluminum housing.
In the conventional apparatus structure, in order to avoid contact between the electronic circuit modules due to thermal expansion, a gap of approximately 0.2 mm is provided in a signal connecting portion between an electronic circuit module 65 and an adjacent electronic circuit module 65' as shown in FIG. 5 and a gap of approximately 0.2 mm is provided in a signal connecting portion between an electronic circuit module 85 and a connection substrate 82, that is, a microstrip line, as shown in FIG. 6. Additionally, the signal connection between adjacent modules is achieved by bonding a gold ribbon 62, 80 onto the wiring by thermocompression bonding or by a combination of ultrasound and thermocompression bonding.
However, this method of connecting results in a state in which the signal line is removed from the ground, thus generating an impedance mismatching in the signal connecting portion. As a result, the gold ribbon wears out quickly when used by itself to minimize this impedance mismatching.
Additionally, the bonding itself is done at a large number of points and therefore requires many steps to perform as well as a much effort to restrict unevenness in, and ensure uniformity of, the bonding.
Further, the work of assembling the electronic circuit modules into a coherent whole also requires many steps because a large number of electronic circuit modules are used, thus requiring a large number of screw holes to be formed in the aluminum housing and a large number of screws to be used in order to mount the electronic circuit modules.
Additionally, as the circuit scale increases the module size also increases, thus limiting freedom of design.